Datasheet

If all is good you will see Done Uploading in the status bar

Uploading to a brand new board/Upload failures

If you are uploading for the first time to a new board, or if upload fails, pres the RESET mini button on the Feather 32u4

Bluefruit when you see the Yellow Arrow lit and the Uploading... text in the status bar. When you see the red LED

pulsing on and off, you know the bootloader is running.